Expanding flash banner

Hello.
I should deliver for my client two swf -files, for a expanding banner. So can thease be files differend pixel size? Or should both be same size as the expanded swf (bigger one), and smaller one with transparent background? Or souhld I i just make smaller and bigger files, and trust that client has coded site so the expandind action is possible?

Quote:
All banners must be built at the expanded size
If this is the only way, is the the expanding swf-file(bigger one) made for maximum content, as the file size of thease to swf-files can be bigger than file-size when using just one swf-file?